Source beam optimization method for improving lithography printability

ABSTRACT

Source beam optimization (SBO) methods are disclosed herein for enhancing lithography printability. An exemplary method includes receiving an integrated circuit (IC) design layout and performing an SBO process using the IC design layout to generate a mask shot map and an illumination source map. The SBO process uses an SBO model that collectively simulates a mask making process using the mask shot mask and a wafer making process using the illumination source map. A mask can be fabricated using the mask shot map, and a wafer can be fabricated using the illumination source map (and, in some implementations, using the mask fabricated using the mask shot map). The wafer includes a final wafer pattern that corresponds with a target wafer pattern defined by the IC design layout. The SBO methods disclosed herein can significantly reduce (or eliminate) variances between the final wafer pattern and the target wafer pattern.

BACKGROUND

Integrated circuit (IC) design becomes more challenging as ICtechnologies continually progress towards smaller feature sizes, such as32 nanometers, 28 nanometers, 20 nanometers, and below. For example,when fabricating IC devices, IC device performance is seriouslyinfluenced by lithography printability capability, which indicates howwell a final wafer pattern formed on a wafer corresponds with a targetwafer pattern defined by an IC design layout. Various methods (such asoptical proximity correction (OPC), mask proximity correction (MPC), andinverse lithography technology (ILT)) have been introduced for enhancinglithography printability, which focus on optimizing a mask used forprojecting an image that corresponds with the target wafer pattern onthe wafer. However, lithography printing capability is also limited bythe wafer fabrication process itself, which uses the optimized mask.Although existing methods for enhancing lithography printability havebeen generally adequate for their intended purposes, they have not beenentirely satisfactory in all respects

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion

FIG. 1 is a simplified block diagram of an integrated circuit (IC)manufacturing system, along with an IC manufacturing flow associatedwith the IC manufacturing system, according to various aspects of thepresent disclosure.

FIG. 2 is a flowchart of a method for fabricating an IC, which can beimplemented by IC manufacturing system of FIG. 1, according to variousaspects of the present disclosure.

FIG. 3 and FIG. 4 are schematic diagrammatic views of an IC designlayout at different IC design stages, which can be implemented in themethod of FIG. 2, according to various aspects of the presentdisclosure.

FIG. 5 is a flowchart of a source beam optimization (SBO) method forgenerating a mask shot map and an illumination source map, which can beimplemented in the method of FIG. 2, according to various aspects of thepresent disclosure.

FIG. 6 is a flowchart of a method for building an SBO model, which canbe implemented in the method of FIG. 5, according to various aspects ofthe present disclosure.

FIG. 7 is a simplified block diagram of an e-beam writer according tovarious aspects of the present disclosure.

FIG. 8 is a simplified block diagram of a lithography system accordingto various aspects of the present disclosure.

FIGS. 9A-9D are fragmentary diagrammatic views of a semiconductor wafer,in portion or entirety, at various wafer fabrication stages according tovarious aspects of the present disclosure.

FIG. 10 is a simplified block diagram of an SBO system, which can beimplemented by the IC manufacturing system of FIG. 1, according tovarious aspects of the present disclosure.

FIG. 11 is a flowchart of a method for fabricating an IC, which can beimplemented by the IC manufacturing system of FIG. 1, according tovarious aspects of the present disclosure.

DETAILED DESCRIPTION

The present disclosure relates generally to lithography processoptimization, and more particularly, to methods for enhancinglithography printability.

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

FIG. 1 is a simplified block diagram of an integrated circuit (IC)manufacturing system 10, along with an IC manufacturing flow associatedwith IC manufacturing system 10, according to various aspects of thepresent disclosure. IC manufacturing system 10 includes a plurality ofentities, such as a design house (or design team) 15, a mask house 20,and an IC manufacturer 25 (for example, an IC fab), that interact withone another in design, development, and manufacturing cycles and/orservices related to manufacturing an IC device 30. The plurality ofentities are connected by a communication network, which may be a singlenetwork or a variety of different networks, such as an intranet and/orInternet, and may include wired and/or wireless communication channels.Each entity may interact with other entities and may provide services toand/or receive services from the other entities. One or more of designhouse 15, mask house 20, and IC manufacturer 25 may be owned by a singlelarge company, and may even coexist in a common facility and use commonresources.

Design house 15 generates an IC design layout 35 (also referred to as anIC design pattern). IC design layout 35 includes various circuitpatterns (represented by geometrical shapes) designed for an IC productbased on specifications of an IC product to be manufactured. The circuitpatterns correspond to geometrical patterns formed in various materiallayers (such as metal layers, dielectric layers, and/or semiconductorlayers) that combine to form IC features (components) of the IC product,such as IC device 30. For example, a portion of IC design layout 35includes various IC features to be formed in a substrate (for example, asilicon wafer) and/or in various material layers disposed on thesubstrate. The various IC features can include an active region, a gatefeature (for example, a gate dielectric or a gate electrode), a sourceregion/feature and a drain region/feature, an interconnection feature(for example, conductive lines and/or conductive vias), bonding padfeatures, other IC feature, or combinations thereof. IC design layout 35may include assist features for providing imaging effects, processenhancements, and/or identification information. In someimplementations, assist features are inserted into IC design layout 35using a geometry proximity correction (GPC) process, similar to anoptical proximity correction (OPC) process used for optimizing maskpatterns (mask layouts). GPC may consider environmental impactsassociated with IC fabrication, including lithography loading effects(such as etching loading effects and patterning loading effectsassociated with exposing and developing processes) and chemicalmechanical polishing process effects arising from pattern densityvariations. Design house 15 implements a proper design procedure to formIC design layout 35. The design procedure may include logic design,physical design, place and route, or combinations thereof. IC designlayout 35 is presented in one or more data files having information ofthe circuit patterns (geometrical patterns). For example, IC designlayout 35 is expressed in a Graphic Database System file format (such asGDS or GDSII). In another example, IC design layout 35 is expressed inanother suitable file format, such as Open Artwork System InterchangeStandard file format (such as OASIS or OAS).

Mask house 20 uses IC design layout 35 to manufacture one or more masks,which are used for fabricating various layers of IC device 30 accordingto IC design layout 35. A mask (also referred to as a photomask orreticle) refers to a patterned substrate used in a lithography processto pattern a wafer, such as a semiconductor wafer. Mask house 20performs mask data preparation 40, where IC design layout 35 istranslated into a form that can be written by a mask writer to generatea mask. For example, IC design layout 35 is translated into machinereadable instructions for a mask writer, such as an electron-beam(e-beam) writer. Mask data preparation 40 generates a mask pattern (masklayout) and corresponding mask shot map, which defines an exposurepattern for printing the mask pattern. The mask pattern is generated byfracturing IC design layout 35 into a plurality of mask features (maskregions) suitable for a mask making lithography process, such as ane-beam lithography process. The fracturing process is implementedaccording to various factors, such as IC feature geometry, patterndensity differences, and/or critical dimension (CD) differences, and themask features are defined based on methods implemented by the maskwriter for printing mask patterns. In some implementations, where ane-beam writer uses a variable-shaped beam (VSB) method for printing maskpatterns, a mask pattern is generated by fracturing IC design layout 35into polygons (such as rectangles or trapezoids), where a correspondingmask shot map includes exposure shot information for each polygon. Forexample, at least one corresponding exposure shot, including an exposuredose, an exposure time, and/or an exposure shape, is defined for eachpolygon. In some implementations, where an e-beam writer uses acharacter projection (CP) method for printing mask patterns, a maskpattern is generated by fracturing IC design layout 35 into characters(typically representing complex patterns) that correspond with a stencilused by the e-beam writer, where a corresponding mask shot map includesexposure shot information for each character. For example, at least onecorresponding exposure shot, including an exposure dose, an exposuretime, and/or an exposure shape, is defined for each character. In suchimplementations, any portions of fractured IC design layout 35 that donot match characters in the stencil can be printed using the VSB method.

Mask data preparation 40 can include various processes for optimizingthe mask pattern, such that a final pattern formed on a wafer (oftenreferred to as a final wafer pattern) by a lithography process using amask fabricated from the mask pattern exhibits enhanced resolution andprecision. For example, mask data preparation 40 can implement opticalproximity correction (OPC), which uses lithography enhancementtechniques to compensate for image distortions and errors, such as thosethat arise from diffraction, interference, or other process effects. OPCcan add assist features, such as scattering bars, serifs, and/orhammerheads, to the mask pattern according to optical models or opticalrules such that, after a lithography process, a final pattern on a waferexhibits enhanced resolution and precision. In some implementations, theassist features can compensate for line width differences that arisefrom different densities of surrounding geometries. In someimplementations, the assist features can prevent line end shorteningand/or line end rounding. OPC can further correct for electron beam(e-beam) proximity effects and/or perform other optimization features.In some implementations, mask data preparation 40 can implement a maskrule check (MRC) process that checks the mask pattern after undergoingan OPC process, where the MRC process uses a set of mask creation rules.The mask creation rules can define geometric restrictions and/orconnectivity restrictions to compensate for variations in ICmanufacturing processes. In some implementations, mask data preparation40 can implement a lithography process check (LPC) process, whichsimulates wafer making processes that will be implemented by ICmanufacturer 25 to fabricate IC device 30. In some implementations, theLPC process simulates an image of a mask based on a generated maskpattern using various LPC models (or rules), which may be derived fromactual processing parameters implemented by IC fab 25. The processingparameters can include parameters associated with various processes ofthe IC manufacturing cycle, parameters associated with tools used formanufacturing the IC, and/or other aspects of the manufacturing process.The LPC process takes into account various factors, such as imagecontrast, depth of focus (“DOF”), mask error sensitivity (“MEEF”), othersuitable factors, or combinations thereof. After a simulatedmanufactured device has been created by LPC, if the simulated device isnot close enough in shape to satisfy design rules, certain steps in maskdata preparation 40, such as OPC and MRC, may be repeated to furtherrefine the IC design layout. It should be understood that mask datapreparation 40 has been simplified for the purposes of clarity, and maskdata preparation 40 can include additional features, processes, and/oroperations for modifying the IC design layout to compensate forlimitations in lithographic processes used by IC fab 25.

Mask house 20 also performs mask fabrication 45, where a mask isfabricated according to the mask pattern and corresponding mask shot mapgenerated by mask data preparation 40. In some implementations, the maskpattern and corresponding mask shot map are modified during maskfabrication 45 to comply with a particular mask writer and/or maskmanufacturer. During mask fabrication 45, a mask making process isimplemented that fabricates a mask based on the mask pattern (masklayout) and corresponding mask shot map. The mask includes a masksubstrate and a patterned mask layer, where the patterned mask layerincludes a final (real) mask pattern. The final mask pattern, such as amask contour, corresponds with the mask pattern (which corresponds witha target wafer pattern provided by IC design layout 35). In someimplementations, the mask is a binary mask. In such implementations,according to one example, an opaque material layer (such as chromium) isformed over a transparent mask substrate (such as a fused quartzsubstrate or calcium fluoride (CaF₂)), and the opaque material layer ispatterned using the mask shot map to form a mask having opaque regionsand transparent regions. In some implementations, the mask is a phaseshift mask (PSM) that can enhance imaging resolution and quality, suchas an attenuated PSM or alternating PSM. In such implementations,according to one example, a phase shifting material layer (such asmolybdenum silicide (MoSi) or silicon oxide (SiO₂)) is formed over atransparent mask substrate (such as a fused quartz substrate or calciumfluoride (CaF₂)), and the phase shifting material layer is patternedusing the mask shot map to form a mask having partially transmitting,phase shifting regions and transmitting regions. In another example, thephase shifting material layer is a portion of the transparent masksubstrate, such that the mask pattern is formed in the transparent masksubstrate using the mask shot map. In some implementations, the mask isan extreme ultraviolet (EUV) mask. In such implementations, according toone example, a reflective layer is formed over a substrate, anabsorption layer is formed over the reflective layer, and the absorptionlayer (such as a tantalum boron nitride (TaBN)) is patterned using themask shot map to form a mask having reflective regions. The substrateincludes a low thermal expansion material (LTEM), such as fused quartz,TiO₂ doped SiO₂, or other suitable low thermal expansion materials. Thereflective layer can include multiple layers formed on the substrate,where the multiple layers include a plurality of film pairs, such asmolybdenum-silicide (Mo/Si) film pairs, molybdenum-beryllium (Mo/Be)film pairs, or other suitable material film pairs configured forreflecting EUV radiation (light). The EUV mask may further include acapping layer (such as ruthenium (Ru)) disposed between the reflectivelayer and the absorption layer. Alternatively, another reflective layeris formed over the reflective layer and patterned using the optimizedmask shot map to form an EUV phase shift mask.

Mask fabrication 45 can implement various lithography processes forfabricating the mask. For example, the mask making process includes alithography process, which involves forming a patterned energy-sensitiveresist layer on a mask material layer using the mask shot map andtransferring a pattern defined in the patterned resist layer to the maskpatterning layer. The mask material layer is an absorption layer, aphase shifting material layer, an opaque material layer, a portion of amask substrate, and/or other suitable mask material layer. Forming thepatterned energy-sensitive resist layer can include forming anenergy-sensitive resist layer on the mask material layer (for example,by spin coating), performing a charged particle beam exposure process,and performing a developing process. Based on the mask shot map, thecharged particle beam exposure process directly “writes” a pattern intothe energy-sensitive resist layer using a charged particle beam, such asan electron beam or an ion beam. Since the energy-sensitive resist layeris sensitive to charged particle beams, exposed portions of theenergy-sensitive resist layer chemically change, and exposed (ornon-exposed) portions of the energy-sensitive resist layer are dissolvedduring the developing process depending on characteristics of theenergy-sensitive resist layer and characteristics of a developingsolution used in the developing process. After development, thepatterned resist layer includes a resist pattern that corresponds withthe mask pattern. The resist pattern is then transferred to the maskmaterial layer by any suitable process, such that a final mask patternis formed in the mask material layer. For example, the mask makingprocess can include performing an etching process that removes portionsof the mask material layer, where the etching process uses the patternedenergy-sensitive resist layer as an etch mask during the etchingprocess. After the etching process, the lithography process can includeremoving the patterned energy-sensitive resist layer from the maskmaterial layer, for example, by a resist stripping process. During theetching process, etching rate and etching behavior may depend on aglobal etching pattern density, often referred to as global etchingloading effect.

IC manufacturer 25, such as a semiconductor foundry, uses the mask (ormasks) fabricated by mask house 20 to fabricate IC device 30. Forexample, a wafer making process is implemented that uses a mask tofabricate a portion of IC device 30 on a wafer, such as a semiconductorwafer. In some implementations, IC manufacturer 25 performs wafer makingprocess numerous times using various masks to complete fabrication of ICdevice 30. Depending on the IC fabrication stage, the wafer can includevarious material layers (for example, dielectric material layers,semiconductor material layers, and/or conductive material layers) and/orIC features (for example, doped regions/features, gate features, and/orinterconnect features) when undergoing the wafer making process. Thewafer making process includes a lithography process, which involvesforming a patterned resist (photoresist) layer on a wafer material layerusing a mask, such as the mask fabricated by mask house 20, andtransferring a pattern defined in the patterned resist layer to thewafer material layer. The wafer material layer is a dielectric materiallayer, a semiconductor material layer, a conductive material layer, aportion of a substrate, and/or other suitable wafer material layer.

Forming the patterned resist layer can include forming a resist layer onthe wafer material layer (for example, by spin coating), performing apre-exposure baking process, performing an exposure process using themask (including mask alignment), performing a post-exposure bakingprocess, and performing a developing process. During the exposureprocess, the resist layer is exposed to radiation energy (such asultraviolet (UV) light, deep UV (DUV) light, or extreme UV (EUV) light)using an illumination source, where the mask blocks, transmits, and/orreflects radiation to the resist layer depending on a final mask patternof the mask and/or mask type (for example, binary mask, phase shiftmask, or EUV mask), such that an image is projected onto the resistlayer that corresponds with the final mask pattern. This image isreferred to herein as a projected wafer image 50. Since the resist layeris sensitive to radiation energy, exposed portions of the resist layerchemically change, and exposed (or non-exposed) portions of the resistlayer are dissolved during the developing process depending oncharacteristics of the resist layer and characteristics of a developingsolution used in the developing process. After development, thepatterned resist layer includes a resist pattern that corresponds withthe final mask pattern. An after development inspection (ADI) 55 can beperformed to capture information associated with the resist pattern,such as critical dimension uniformity (CDU) information, overlayinformation, and/or defect information.

Transferring the resist pattern defined in the patterned resist layer tothe wafer material layer is accomplished in numerous ways, such that afinal wafer pattern 60 is formed in the wafer material layer. Forexample, the wafer making process can include performing an implantationprocess to form various doped regions/features in the wafer materiallayer, where the patterned resist layer is used as an implantation maskduring the implantation process. In another example, the wafer makingprocess can include performing an etching process that removes portionsof the wafer material layer, where the etching process uses thepatterned resist layer as an etch mask during the etching process. Afterthe implantation process or the etching process, the lithography processincludes removing the patterned resist layer from the wafer, forexample, by a resist stripping process. In yet another example, thewafer making process can include performing a deposition process thatfills openings in the patterned resist layer (formed by the removedportions of the resist layer) with a dielectric material, asemiconductor material, or a conductive material. In suchimplementations, removing the patterned resist layer leaves a wafermaterial layer that is patterned with a negative image of the patternedresist layer. An after etch inspection (AEI) is performed to captureinformation, such as critical dimension uniformity (CDU), associatedwith the final wafer pattern 60 formed in the wafer material layer.

Ideally, final wafer pattern 60 matches a target wafer pattern providedby IC design layout 35. However, due to various factors associated withthe mask making process and the wafer making process, the final maskpattern formed on the mask often varies from the mask pattern (generatedfrom IC design layout 35 for the target wafer pattern), causing finalwafer pattern 60 formed on the wafer to vary from the target waferpattern. For example, mask writing blur (such as e-beam writing blur)and/or other mask making factors cause variances between the final maskpattern and the mask pattern, which causes variances between final waferpattern 60 (fabricated using the mask having the final mask pattern) andthe target wafer pattern. Various factors associated with the wafermaking process (such as resist blur, mask diffraction, projectionimaging resolution, acid diffusion, etching bias, and/or other wafermaking factors) further exacerbate the variances between final waferpattern 60 and the target wafer pattern. The following discussionproposes various optimization techniques for enhancing the mask maskingprocess and the wafer making process, thereby minimizing variancesbetween final wafer pattern 60 and the target wafer pattern andenhancing lithography printability.

FIG. 2 is a flowchart of a method 100 for fabricating an integratedcircuit (IC), which can be implemented by IC manufacturing system 10 ofFIG. 1, according to various aspects of the present disclosure. Designhouse 15, mask house 20, and/or IC manufacturer 25 can perform method100. In some implementations, design house 15, mask house 20, and/or ICmanufacturer 25 collaborate to perform method 100. At block 110, method100 includes receiving an IC design layout, such as IC design layout 35,for a target wafer pattern. The IC design layout is presented in one ormore data files having information of the target pattern. For example,the IC design layout is received in a GDSII file format or an OASIS fileformat. The IC design layout includes various circuit patterns(represented by geometrical shapes) designed for an IC product based onspecifications of an IC product to be manufactured. The circuit patternscorrespond to geometrical patterns formed in various material layers(such as metal layers, dielectric layers, and/or semiconductor layers)that combine to form IC features of the IC product. For example, aportion of the IC design layout includes various IC features to beformed in a substrate (for example, a silicon substrate) and/or invarious material layers disposed on the substrate. FIG. 3 is a schematicdiagrammatic view of an IC design layout 120 according to variousaspects of the present disclosure. The IC design layout 120 includesvarious geometrical patterns that represent IC features (also referredto as main features), such as an IC feature 122, an IC feature 124, anIC feature 126, and an IC feature 128. The main features in the ICdesign layout 120 constitute a portion of an IC device, such as ICdevice 30, that is to be formed or defined in a material layer of awafer. Each main feature represents an active region, a gate feature(for example, a gate electrode), a source region/feature and a drainregion/feature, an interconnection feature, a bonding pad feature, orother IC features.

Turning again to FIG. 2, at block 130, method 100 can include modifyingthe IC design layout for the target wafer pattern, thereby generating amodified IC design layout for the target wafer pattern. In someimplementations, dummy features are added to the IC design layout, suchas IC design layout 120, to optimize a final wafer pattern fabricated ona wafer during IC fabrication. FIG. 4 is a schematic diagrammatic viewof an IC design layout, such as IC design layout 120, after undergoing amodification (optimization) process according to various aspects of thepresent disclosure. In FIG. 4, dummy features 132 are inserted into ICdesign layout 120. In some implementations, dummy features 132 are addedto IC design layout 120 to tune local pattern densities, such thatpattern density varies less from location to location, thereby reducingprocessing variations (for example, by providing polishing uniformity,etching uniformity, and/or thermal annealing uniformity) and/or otherunexpected effects (such as mechanical stress). For example, IC designlayout 120 can include a target wafer pattern that defines variousactive regions to be formed on a wafer. The active regions can bedefined on the wafer by forming a patterned layer over the wafer (forexample, implementing a lithography exposure and development process toform a patterned resist layer over the wafer), forming trenches in thewafer (for example, etching the wafer using the patterned resist layeras an etch mask), filling the trenches with a dielectric material, andperforming a CMP process to form isolation features that define theactive regions of the wafer. The CMP process, which removes excessivedielectric material and planarizes a top surface of the wafer, oftenintroduces dishing and/or erosion effects. Dummy features 132 added toIC design layout 120 can tune a pattern density, thereby reducing suchside effects and improving CMP process results. In another example,where IC design layout 120 includes a target wafer pattern that definessource/drain features to be formed on a wafer, dummy features 132 can beadded to IC design layout 120 to reduce thermal annealing variationsfrom location to location, thereby improving a thermal annealing process(implemented, for example, to activate ion implanted dopants) applied tothe wafer. In yet another example, where IC design layout 120 includes atarget wafer pattern that defines conductive lines of an interconnectionstructure, dummy features 132 can be added to IC design layout 120 invarious regions of the wafer, such as die-corner-circuit-forbiddenregions, to relieve corner chip stresses. Other features may be added toIC design layout 120 in appropriate locations, such as in frame regionsof the wafer. Such features include mask identification numbers (forexample, barcodes), alignment marks, test patterns, other features, orcombinations thereof depending on various IC fabrication usages and/orconsiderations.

Turning again to FIG. 2, at block 140, method 100 includes performing asource beam optimization (SBO) process using the IC design layout forthe target wafer pattern (which is received at block 110 or generated atblock 130) to generate a mask shot map and an illumination source map.The mask shot map is associated with a mask making process, where themask shot map defines an exposure pattern for printing (writing) a finalmask pattern on a mask during the mask making process. The final maskpattern corresponds with a mask pattern that is based on the targetwafer pattern of the IC design layout. The exposure pattern can definemask shot information for each mask region (also referred to as maskfeature or mask polygon) of the mask pattern. In some implementations,mask shot information includes exposure dose (energy) and/or exposureshape required for printing a respective mask feature of the maskpattern. In some implementations, mask shot information may define morethan one mask shot (exposure shot) for a mask feature, which definesexposure dose (energy) and/or exposure shape. In contrast, theillumination source map is associated with a wafer making process, wherethe illumination source map defines illumination source optics forilluminating a mask when printing a final wafer pattern on a waferduring the wafer making process. The final wafer pattern correspondswith the final mask pattern, such as an image of the final mask patternprojected onto the wafer under the illumination source optics. Theillumination source optics can define illumination information, such asan illumination source shape, which represents a distribution of anglesof radiation falling on a mask and/or wafer. In some implementations,the illumination source map can define geometric shapes (for example,annular, quadrapole, or dipole) representing a distribution of angles ofradiation. For ease of discussion, block 140 is generally referred tohereinafter as SBO process 140.

FIG. 5 is a flowchart of SBO process 140, which can be implemented inmethod 100, according to various aspects of the present disclosure. Atblock 142, SBO process 140 includes receiving a mask shot map and anillumination source map. In some implementations, the mask shot mapand/or the illumination map are generated based on historical dataand/or simulated data associated with mask making processes and/or wafermaking processes, such as those used to generate a target wafer patterndefined by the IC design layout. At block 144, an SBO model is used tosimulate a final wafer pattern based on the mask shot map and theillumination source map. For example, the SBO model predicts the finalwafer pattern by collectively simulating (1) a mask making process thatuses the mask shot map to fabricate a mask and (2) a wafer makingprocess that uses the illumination source map (and, in someimplementations, the mask fabricated using the mask shot map). At block146, SBO process 140 adjusts (tunes) the mask shot map and theillumination source map until the simulated final wafer pattern fits atarget wafer pattern of an IC design layout, such as that received atblock 110 or generated at block 130. In some implementations, anexposure pattern of the mask shot map is tuned (adjusted), andillumination source optics defined by the illumination source map aretuned (adjusted), such as individual exposure doses and/or individualexposure shapes. In some implementations, various parameters associatedwith the wafer making process and the mask making process remain fixed,while SBO process 140 varies exposure conditions associated with themask making process and the wafer making process. At block 148, SBOprocess 140 outputs an optimized mask shot map and an optimizedillumination source map. In some implementations, a mask making processuses the optimized mask shot map to fabricate a mask. In someimplementations, during the wafer making process, the wafer makingprocess uses the optimized illumination source map to illuminate themask fabricated from the optimized mask shot map. Additional steps canbe provided before, during, and after SBO process 140, and some of thesteps described can be moved, replaced, or eliminated for additionalembodiments of SBO process 140.

Considering FIG. 2 and FIG. 5, SBO process 140 and its associated SBOmodel are further described according to various aspects of the presentdisclosure. SBO process 140 is a model-based process that tunes(adjusts) a given mask shot map m_(f) and a given illumination sourcemap S according to an SBO model that minimizes (or eliminates) anydifferences between a desired target wafer pattern (T) (in someimplementations, a set of desired target wafer patterns T) and apredicted final wafer pattern P (in some implementations, a set ofsimulated final wafer patterns P). In particular, through an iterativeprocess, the SBO model optimizes mask shot map m_(f) and illuminationsource map S using an optimization (minimization) problem that minimizesa difference between predicted final wafer pattern P and target waferpattern T:

$\begin{matrix}{{\min\limits_{S,m_{f}}{{P - T}}},} & {{Equation}\mspace{14mu}(1)}\end{matrix}$where target wafer pattern T is defined by the IC design layout (or ICdesign layouts) received at block 110 and/or block 130 (though thepresent disclosure contemplates other sources for target wafer patternT) and predicted final wafer pattern P is generated by the SBO modelcollectively simulating (1) a mask making process that uses mask shotmap m_(f) to fabricate a mask and (2) a wafer making process that usesillumination source map S (and, in some implementations, the maskfabricated using mask shot map m_(f)). During the iterative process, theSBO model compares predicted (simulated) final wafer pattern P to targetwafer pattern T, tuning (adjusting) mask shot map m_(f) and illuminationsource map S until predicted final wafer pattern P is best fits targetwafer pattern T. In some implementations, predicted final wafer patternP matches target wafer pattern T when a simulated final wafer patterncontour matches a target wafer pattern contour, or when any differencetherebetween is less than a defined tolerance range. SBO process 140thus co-optimizes mask shot map m_(f) and illumination source map S,such that predicted final wafer pattern P matches target wafer patternT.

Predicted final wafer pattern P can be represented two-dimensionally inan x-dimension and a y-dimension by predicted final wafer patternP(x,y), where predicted final wafer pattern P(x,y) defines a contour ofa final wafer pattern formed in a wafer material layer after simulatinga wafer making process on the wafer. The simulated wafer making processincludes simulating any process implemented to form a pattern in a wafermaterial layer, such as the lithography process described above withreference to FIG. 1. For example, the simulated wafer making processincludes forming a patterned resist layer on a wafer material layer andtransferring a pattern defined in the patterned resist layer to thewafer material layer. Such processing can include an exposure process, adeveloping process, and an etching process. In some implementations,predicted final wafer pattern P(x,y) represents a pattern formed in thewafer material layer after a resist pattern (formed in the resist layer)is transferred to the wafer material layer (for example, after anexposure process, a developing process, and an etching process).Alternatively, in some implementations, predicted final wafer patternP(x,y) represents the resist pattern formed in the resist layer disposedon the wafer material layer (for example, after an exposure process anda developing process).

A wafer patterning function Γ defines characteristics and/or behaviorsassociated with the simulated wafer making process, such as thelithography process, used to form predicted final wafer pattern P(x,y).Wafer patterning function Γ can account for characteristics and/orbehaviors associated with the patterned resist layer formed over thewafer (which includes a resist pattern that corresponds with a finalmask pattern of the mask) and/or the patterned wafer. For example, waferpatterning function Γ simulates characteristics and/or behaviors of apatterned resist layer formed on the wafer during the lithographyprocess, such as a response of the resist layer during a pre-exposurebaking process, a response of the resist layer during an exposingprocess (such as characteristics and/or behaviors related to reactionsof the resist layer in response to illumination (for example, radiationenergy) used during the exposure process), a response of the resistlayer during a post-exposure baking process, a response of the resistlayer during a developing process, and/or a response of the resist layerduring any other process associated with the wafer making process. Waferpatterning function Γ can further simulate characteristics and/orbehaviors associated with transferring the pattern in the patternedresist layer to the wafer material layer, such as etching bias from anetching process.

Wafer patterning function Γ is a function of a projected wafer image I(in some implementations, a set of projected wafer images I), whichsimulates imaging of a mask on a resist layer during an exposure processassociated with the lithography process. Thus, predicted final waferpattern P(x,y) depends on projected wafer image I as expressed by:P(x,y)=Γ(I(x,y)),  Equation (2)where I(x,y) defines a projected wafer image having a two-dimensionalprofile, such as a contour, defined in an x-dimension and a y-dimension.In some implementations, an exposure process is simulated to generateprojected wafer image I(x,y). The exposure process includes illuminatinga mask having a final mask pattern with radiation (using an illuminationsource), such that an image corresponding with the final mask pattern isprojected onto a resist layer. The illumination source illuminates themask based on illumination source map S. In such implementations,projected wafer image I(x,y) is a function of illumination source map S(in some implementations, a set of illumination source maps S) and afinal mask pattern m (in some implementations, a set of final maskpatterns m), such that:I=I(x,y)=I(S(x,y),m(x,y)),  Equation (3)where S(x,y) represents a two-dimensional illumination source mapdefined in an x-dimension and a y-dimension, and m(x,y) represents atwo-dimensional final mask pattern defined in the x-dimension and they-dimension. Illumination source map S(x,y) defines illumination sourceoptics for illuminating the mask during the simulated wafer makingprocess, and final mask pattern m(x,y) defines a mask contour formed onthe mask by the simulated mask making process. A mask patterningfunction (Φ) defines characteristics and/or behaviors associated withthe mask making process used to simulate final mask pattern m(x,y),where the mask making process uses mask shot map m_(f) and acorresponding mask pattern (mask layout) to form final mask patternm(x,y), such that final mask pattern m(x,y) can be expressed as:m(x,y)=Φ(m _(f)(x,y)),  Equation (4)where m_(f)(x,y) represents a two-dimensional mask shot map defined inan x-dimension and a y-dimension. Mask shot map m_(f)(x,y) defines anexposure pattern for fabricating the mask during the simulated maskmaking process, where the exposure pattern can indicate exposure dosesand/or exposure shapes (for example, in the x-dimension and they-dimension) for corresponding mask regions (or mask polygons) of themask pattern. Thus, projected wafer image I on the wafer (in particular,on the resist layer disposed on the wafer) is a function of mask makingfunction Φ, such that:I=I(x,y)=I(S(x,y),Φ(m _(f)(x,y)),  Equation (5)and predicted final wafer pattern P can be predicted by:P(x,y)=Γ(I(S(x,y),Φ(m _(f)(x,y))).  Equation (6)In some implementations, where final mask pattern m(x,y) is transferredto the mask by an e-beam writing process, mask shot map m_(f)(x,y) is ane-beam shot map that defines an e-beam exposure pattern for fabricatingthe mask, where the e-beam exposure pattern indicates exposure dosesand/or exposure shapes for corresponding mask regions of the maskpattern.

Considering all of the above factors associated with the mask makingprocess (associated with mask patterning function Φ) and the wafermaking process (associated with projected imaging function I and waferpatterning function Γ) expressed in Equations 1-6, the SBO model'soptimization (minimization) problem becomes:

$\begin{matrix}{{\min\limits_{S,m_{f}}{{{\Gamma\left( {I\left( {{S\left( {x,y} \right)},{\Phi\left( {m_{f}\left( {x,y} \right)} \right)}} \right)} \right)} - T}}},} & {{Equation}\mspace{14mu}(7)}\end{matrix}$which minimizes a difference between predicted final wafer pattern P andtarget wafer pattern T by adjusting mask shot map m_(f) and illuminationsource map S. SBO process 140 then uses the SBO model in theoptimization (minimization) problem to vary illumination source map S(in other words, vary illumination conditions of the wafer makingprocess) and mask shot map (vary exposure conditions of the mask makingprocess) to best fit predicted wafer pattern P to target wafer patternT.

In some implementations, the SBO model simulates the mask making processassuming that illumination source S is represented by a rectangulararray and mask shot map m_(f) is represented by a sum of mask shots p(for example, a sum of e-beam shots), such that mask pattering functionΦ can be represented by a convolution operation ⊗ and final mask patternm(x,y) is expressed as:

$\begin{matrix}{{{m\left( {x,y} \right)} = {{\Phi\left( {m_{f}\left( {x,y} \right)} \right)} = {{\Phi\left( {\sum\limits_{i = 1}^{q}{p_{i}\left( {x,y} \right)}} \right)} = {\sum\limits_{i = 1}^{q}{{p_{i}\left( {x,y} \right)} \otimes {G\left( {x,y} \right)}}}}}},} & {{Equation}\mspace{14mu}(8)}\end{matrix}$where q represents a number of mask regions (also referred to as maskpolygons or mask features) of the mask pattern (mask layout), p_(i) ismask shot information for an ith mask region of the mask pattern definedtwo-dimensionally in an x-dimension and a y-dimension, and G(x,y) is aGreen's function that represents mask making behavior and/or mask makingcharacteristics associated with the mask pattern. Mask shot p_(i) caninclude exposure dose and/or exposure shape information. In suchimplementations, the SBO optimization (minimization) problem becomes:

$\begin{matrix}{\min\limits_{S,m_{f}}{{\Gamma\left( {{I\left( {{S\left( {x,y} \right)},{{\sum\limits_{i = 1}^{q}{{p_{i}\left( {x,y} \right)} \otimes {G\left( {x,y} \right)}}} - T}} \right.},} \right.}}} & {{Equation}\mspace{14mu}(9)}\end{matrix}$which minimizes a difference between predicted final wafer pattern P andtarget wafer pattern T by adjusting mask shot information includingexposure dose and/or exposure shape (and thus generating mask shot mapm_(f)) and illumination source map S. In some implementations, SBOminimizes any differences between predicted final wafer pattern P andtarget wafer pattern T using a subset of the q mask regions of the maskpattern.

In some implementations, the SBO model simulates predicted final waferpattern P using a resist model (RM), such that predicted final waferpattern P is simulated by:P(x,y)=Γ(I(x,y),RM),  Equation(10)where resist model RM models resist image formation. In someimplementations, resist model RM represents resist behavior and/orresist characteristics associated with the resist layer on whichprojected wafer image I(x,y) is formed during the wafer making process.In such implementations, the SBO optimization (minimization) problembecomes:

$\begin{matrix}{\min\limits_{S,m_{f}}{{\Gamma\left( {{I\left( {{S\left( {x,y} \right)},{\sum\limits_{i = 1}^{q}{{p_{i}\left( {x,y} \right)} \otimes {G\left( {x,y} \right)}}},{{RM} - T}} \right.},} \right.}}} & {{Equation}\mspace{14mu}(11)}\end{matrix}$which minimizes a difference between predicted final wafer pattern P andtarget wafer pattern T by adjusting mask shot information includingexposure dose and/or exposure shape (and thus generating mask shot mapm_(f)) and illumination source map S. In some implementations, whenusing resist model RM, SBO minimizes any differences between predictedfinal wafer pattern P and target wafer pattern T using a subset of the qmask regions of the mask pattern.

During SBO process 140, the minimization process can implement a costfunction (also referred to as a loss function) to minimize a differencebetween target wafer pattern T and predicted final wafer pattern P. Forexample, in some implementations, a cost function is defined accordingto an edge placement error, where SBO process 140 optimizes mask shotmap m_(f) and illumination source map S using an optimization problemthat minimizes a sum of edge placement errors between predicted finalwafer pattern P and target wafer pattern T:

$\begin{matrix}{\min\limits_{S,m_{f}}{\left\{ {\sum\limits_{j = 1}^{n}{{{EPE}\left( {x_{j},y_{j}} \right)}}} \right\}.}} & {{Equation}\mspace{14mu}(12)}\end{matrix}$In Equation (12), where target wafer pattern T and predicted final waferpattern P have n corresponding locations (points), an edge placementerror function (EPE) defines a difference between an edge of targetwafer pattern T and an edge of predicted final wafer pattern P at aj^(th) corresponding location given by a respective x-coordinate (x_(j))and a respective y-coordinate (y_(j)). In some implementations, theEPE-based optimization problem (Equation (12)) minimizes a sum of edgeplacement errors over a subset of the n corresponding locations. Inanother example, in some implementations, a cost function is definedaccording to an area difference, where SBO process 140 optimizes maskshot map m_(f) and illumination source map S to minimize a sum of areadifferences between predicted final wafer pattern P and target waferpattern T:

$\begin{matrix}{\min\limits_{S,m_{f}}{\left\{ {\sum\limits_{k = 1}^{m}{{\Delta\;{{Area}\left( {P_{k} - T_{k}} \right)}}}} \right\}.}} & {{Equation}\mspace{14mu}(13)}\end{matrix}$In Equation (13), where target wafer pattern T and predicted final waferpattern P have m corresponding regions (or corresponding polygons), anarea function (ΔArea) defines a difference between an area of a k^(th)corresponding region (or a k^(th) corresponding polygon) of target waferpattern T and predicted final wafer pattern P. In some implementations,the area difference based optimization problem (Equation (13)) minimizesa sum of area differences over a subset of the m corresponding regions(or corresponding polygons).

The SBO model is built using historic data from mask making processesand wafer making processes. Various behaviors associated with the SBOmodel (such as mask patterning function Φ, projected imaging function I,and wafer patterning function Γ) can be individually or collectivelycalibrated depending on IC design and manufacturing considerations.Alternatively, in some implementations, the SBO model is built usingsimulated data for mask making processes and wafer making processes.FIG. 6 is a flowchart of a method 150 for generating an SBO model, suchas the SBO model described with reference to FIG. 2 and FIG. 5,according to various aspects of the present disclosure. In someimplementations, method 150 is implemented by an entity of ICmanufacturing system 10 of FIG. 1, such as mask house 20. Additionalsteps can be provided before, during, and after method 150, and some ofthe steps described can be moved, replaced, or eliminated for additionalembodiments of method 150.

At block 152, method 150 includes collecting historic data from a maskmaking process and a wafer making process. In some implementations,historic mask making process data includes data associated with maskwriting processes (such as e-beam writing processes) and/or etchingprocesses used to form final mask patterns in masks, where the finalmask patterns correspond with mask patterns generated from IC designlayouts for target wafer patterns. In furtherance of suchimplementations, the historic mask making process data can be collectedfrom a corresponding lithography process (such as an e-beam lithographyprocess) and/or an etch process. In some implementations, historic wafermaking process data includes data from lithography processes used toform final wafer patterns in wafers, where the final wafer patternscorrespond with the final mask patterns. In furtherance of suchimplementations, the historic wafer making process data can be collectedfrom a corresponding lithography process, an etch process, and/or an ionimplantation process.

At block 154, method 150 builds an SBO model using the historic data ofthe mask making process and the wafer making process. Any suitableprocedure is implemented for effectively building the SBO model. In someimplementations, the SBO model is built by constructing a singlemathematical model that collectively simulates the mask making processand the wafer making process as a function of a given mask shot map anda given illumination source map, and determining coefficients or otherparameters for the mathematical model using the historic data (forexample, by performing a least squares fit). In some implementations,the SBO model is constructed according to various inputs, such astheoretical analysis of mask making processes and wafer makingprocesses, empirical formulas, engineering inputs, other suitableinputs, or combinations thereof.

At block 156, method 150 can maintain the SBO model. Since the SBO modelsimulates a mask making process and a wafer making process, the SBOmodel is a function of both mask making processes, wafer makingprocesses, and corresponding mask making and wafer making systems and/ortools (for example, electron-beam lithography system/tool, opticallithography system/tool, etching system/tool, and so on). The maskmaking process and the wafer making process may change over time due tovarious factors (for example, chemical lifetime or characteristics ofchemical batches associated with lithography processes). Thecorresponding mask making tools and wafer making tools may also changeover time (for example, different calibration settings or duringextended times between calibrations). Accordingly, as method 150continuously collects historic data from the mask making processes andthe wafer making processes at block 152, SBO model can be adjusted basedon recently collected historic IC fabrication data. For example,recently collected historic IC fabrication data can be implemented todetermine (adjust) coefficients of the SBO model to compensate forshifts (changes) in the mask making process and the wafer makingprocess. In some implementations, the SBO model is updated at a givenfrequency. In some implementations, updating the SBO model is triggeredwhen shifts in the mask making process and wafer making processes areobserved (for example, from statistical process control charts).

Returning to FIG. 2, method 100 can continue at block 160, where a maskis fabricated using an optimized mask shot map, such as optimized maskshot map m_(f) generated by SBO process 140. The mask includes a masksubstrate and a patterned mask layer, which is designed based on variousmask technologies. For example, mask house 20 of IC manufacturing system10 can implement a mask making process, described in detail above withreference to FIG. 1, using the optimized mask shot map to form thepatterned mask layer. In some implementations, an e-beam lithographysystem (also referred to as an e-beam writer or an e-beam writer system)performs an e-beam lithography process to pattern a mask with a finalmask pattern, where the final mask pattern corresponds with the targetpattern of the IC design layout. The e-beam lithography process caninclude forming an e-beam sensitive resist layer over a mask materiallayer, and exposing the e-beam sensitive resist layer by scanning ane-beam across the e-beam sensitive resist layer based on the optimizedmask shot map (generated by SBO process 140). During the exposingprocess, a dose and/or shape of each e-beam exposure shot (mask shot)for forming respective mask features can be tuned based on the optimizedmask shot map. Exposed portions of the e-beam sensitive resist layerchemically change, enabling selective removal of exposed or non-exposedportions of the e-beam sensitive resist layer during a developingprocess, and thereby forming a patterned e-beam sensitive resist layer.The e-beam lithography process can further include performing an etchingprocess that uses the patterned e-beam sensitive resist layer as an etchmask to remove portions of the mask material layer (such as an opaquelayer, a phase shifting material layer, an absorption layer, or aportion of a mask substrate), thereby forming a final mask pattern inthe mask material layer by transferring a pattern defined in thepatterned e-beam sensitive resist layer to the mask material layer. Thepatterned e-beam sensitive resist layer can then be removed, forexample, by a resist stripping process. Alternatively, in someimplementations, the e-beam lithography process directly writes thefinal mask pattern to the mask material layer based on the optimizedmask shot map, omitting the processing involved with the e-beamsensitive resist layer.

FIG. 7 is a simplified block diagram of an e-beam writer 200, which canbe implemented for fabricating masks at block 160, according to variousaspects of the present disclosure. Based on an optimized mask shot map(such as that generated by SBO process 140 of method 100), e-beam writer200 can fabricate a mask 202 by writing an IC pattern on an e-beamsensitive resist layer 204 formed on a mask substrate 206. In someimplementations, e-beam writer 200 receives the optimized mask shot mapin the form of a pattern writing instruction set (for example, from apattern generator). In FIG. 7, mask 202 is positioned on a stage 208within a chamber 210. An e-beam source 212 generates an electron beam(s)214. In some implementations, e-beam source 212 is an electron gun withan electron generating mechanism (for example, thermal electronemission). In a particular example, the electron gun includes a tungsten(or other suitable material) filament designed and biased to thermallyemit electrons. Electron beam 214 is directed and positioned on mask 202(in particular, e-beam sensitive resist layer 204) by an e-beam column216. In some implementations, e-beam column 216 includes lenses forfocusing electrons generated by e-beam source 212 to achieve desiredimaging effect (for example, electrostatic lenses and/or electromagneticlenses), apertures for defining a shape and/or distribution of electronbeam 214, a deflection system for scanning electron beam 214 across mask202 (for example, in a vector mode or a raster mode), and other e-beamcolumn components. In some implementations, e-beam source 212 isconsidered a portion of e-beam column 216. In some implementations, thedeflection system is a scanner that magnetically (for example, usingconductive coils) or electrostatically (for example, using conductiveplates) deflects electron beam 214 in two orthogonal directions, suchthat electron beam 214 is scanned over a surface of mask 202, such as asurface of e-beam sensitive resist layer 204. A pump unit 218 cangenerate a vacuum environment or other suitable environment in chamber210 during an e-beam lithography process. FIG. 7 has been simplified forthe sake of clarity to better understand the inventive concepts of thepresent disclosure. Additional features can be added in e-beam writer200, and some of the features described below can be replaced oreliminated for additional embodiments of e-beam writer 200.

Returning to FIG. 2, other processing steps may follow after fabricatingthe mask. For example, at block 160, method 100 includes fabricating awafer. At block 170, method 100 includes fabricating a wafer using anoptimized illumination source map (generated by the SBO process at block140) and/or optimized mask (generated by the mask making process atblock 160). For example, IC fab 25 of IC manufacturing system 10 canimplement a wafer making process, described in detail above withreference to FIG. 1, using the optimized illumination source map to forma patterned wafer material layer. In some implementations, a lithographysystem performs a lithography process to pattern a wafer material layerwith a final wafer pattern, where the final wafer pattern correspondswith the target pattern of the IC design layout. The lithography processcan include forming a resist layer on the wafer material layer (forexample, by spin coating), and exposing the resist layer by illuminatinga mask (such as the mask fabricated at block 160) based on the optimizedillumination source map (generated by SBO process 140). During theexposure process, illumination source optics are configured toilluminate the mask with radiation energy (such as UV light, DUV light,or EUV light). Various components of the lithography system can be tunedto configure the illumination source optics as defined by anillumination source map. The mask blocks radiation from and/or transmitsradiation to the resist layer depending on a type of the mask (forexample, binary mask, phase shift mask, or EUV mask), a final maskpattern of the mask, and the illumination source optics used toilluminate the mask with the radiation energy, such that an image isprojected onto the resist layer that corresponds with the final maskpattern. Exposed portions of the resist layer chemically change,enabling selective removal of exposed or non-exposed portions of theresist layer during a developing process, and thereby forming apatterned resist layer. The lithography process can further includeperforming an etching process that uses the patterned resist layer as anetch mask to remove portions of the wafer material layer (such as adielectric material layer, a semiconductor material layer, a conductivematerial layer, or a portion of a wafer substrate), thereby forming afinal wafer pattern in the wafer material layer by transferring apattern defined in the patterned resist layer to the wafer materiallayer. The patterned resist layer can then be removed, for example, by aresist stripping process.

FIG. 8 is a simplified block diagram of a lithography system 250, whichcan be implemented for fabricating wafers at block 170, according tovarious aspects of the present disclosure. Based on an optimizedillumination source map (such as that generated by SBO process 140 ofmethod 100), lithography system 250 can fabricate a wafer forming an ICpattern on a wafer material layer. In some implementations, lithographysystem 250 receives optimized illumination source map in the form of anillumination source optics instruction set. In FIG. 8, lithographysystem 250 includes an illumination source 252, illumination optics 254,a mask 256, projection optics 258, and a target 260 such as asemiconductor wafer on a substrate stage. Illumination source 252 emitsradiation of a suitable wavelength, such as UV radiation, DUV radiation,or EUV radiation. In some implementations, illumination source 252 caninclude a mercury lamp for providing UV radiation, such as 436 nm(G-line) and 365 nm (I-line). In some implementations, illuminationsource 252 can include an excimer laser for providing DUV radiation,such as 248 nm, 193 nm and 157 nm. An example of excimer laser includesa krypton fluoride (KrF) excimer laser, an argon fluoride (ArF) excimerlaser, or a fluoride (F₂) excimer laser. Illumination optics 254collect, guide, and direct the radiation emitted by illumination source252 to mask 256. In some implementations, illumination source 252 andillumination optics 254 are configured based on the optimizedillumination source map (for example, generated by SBO process 140).Mask 256 transmits, absorbs, and/or reflects the radiation depending ona final mask pattern of mask 256, along with mask technologies used tofabricate mask 256, thereby providing patterned radiation. In someimplementations, mask 256 is a mask fabricated by method 100 at block160, which uses a mask shot map generated by SBO process 140. Projectionoptics 258 collect, guide, and direct the patterned radiation to target260, such that an image of mask 256 (corresponding with the final maskpattern) is projected onto target 260. Illumination optics 254 andprojection optics 258 include refractive optics (such as one or morelenses), reflective optics (such as one or more mirrors), and/or anyother illumination/projection components for facilitating illuminationoptics 254 and projection optics 258 in collecting, guiding, anddirecting radiation from illumination source 252 to target 260. In someimplementations, apertures of various lenses of illumination optics 254can be adjusted based on the optimized illumination source map. Target260 includes a wafer having a radiation sensitive layer (for example, aresist layer) disposed thereover, where portions of the radiationsensitive layer exposed to the radiation chemically change. Target 260may be held on a wafer stage, which provides control of a position oftarget 260 within lithography system 250, such that an image of mask 256can be scanned onto target 260 in a repetitive fashion (though otherlithography methods are possible). Lithography system 250 can includeadditional items depending on implemented lithography processtechnologies. FIG. 8 has been simplified for the sake of clarity tobetter understand the inventive concepts of the present disclosure.Additional features can be added in lithography system 250, and some ofthe features described below can be replaced or eliminated foradditional embodiments of lithography system 250.

FIGS. 9A-9D are fragmentary diagrammatic views of a semiconductor wafer270, in portion or entirety, at various wafer fabrication stages, suchas those associated with block 170 of method 100, according to variousaspects of the present disclosure. In FIG. 9A, semiconductor wafer 270includes a semiconductor substrate 275, such as a silicon substrate.Alternatively or additionally, semiconductor substrate 275 includesother semiconductor materials, such as germanium, silicon germanium,silicon carbide, or gallium arsenide. A wafer material layer 280 isformed over semiconductor substrate 275. In some implementations, wafermaterial layer 280 is a dielectric layer, a semiconductor layer, or aconductive layer. Depending on wafer fabrication stage, semiconductorwafer 270 can include various material layers (for example, dielectricmaterial layers, semiconductor material layers, and/or conductivematerial layers) and/or IC features (for example, dopedregions/features, gate features, and/or interconnect features) whenundergoing the wafer making process. The wafer making process patternswafer material layer 280 using a lithography process, which can includea resist coating process, an exposure process, and a developing processas described in detail herein. In FIG. 9B, a lithography patterningprocess forms a patterned resist layer 285 over wafer material layer280. In some implementations, the lithography patterning processincludes exposing a resist layer in a lithography system (such aslithography system 250 of FIG. 8) using a mask fabricated using anoptimized mask shot map, such as the mask fabricated at block 160 ofmethod 100. The wafer making process can continue by transferring apattern defined in patterned resist layer 285 to wafer material layer280. For example, in FIG. 9C, an etching process is performed thatremoves portions of wafer material layer 280 using patterned resistlayer as an etch mask. In FIG. 9D, the patterned resist layer may beremoved by resist stripping process. FIGS. 9A-9C have been simplifiedfor the sake of clarity to better understand the inventive concepts ofthe present disclosure. Additional features can be added insemiconductor wafer 270, and some of the features described below can bereplaced, modified, or eliminated in other embodiments of semiconductorwafer 270.

FIG. 10 is a simplified block diagram of a source beam optimization(SBO) system 300, which can be implemented by IC manufacturing system 10of FIG. 1, according to various aspects of the present disclosure. Insome implementations, mask house 20 implements SBO system 300, where SBOsystem 300 is operable to perform functionalities described inassociation with mask data preparation 40 of FIG. 1. SBO system 300includes both hardware and software integrated to perform variousoperations and/or functions for generating a mask shot map and anillumination source map, as described herein. In some implementations,an SBO process, such as SBO process 140, may be implemented as softwareinstructions executing on SBO system 300. FIG. 10 has been simplifiedfor the sake of clarity to better understand the inventive concepts ofthe present disclosure. Additional features can be added in SBO system300, and some of the features described below can be replaced oreliminated for additional embodiments of SBO system 300.

SBO system 300 includes a processor 302 that is communicatively coupledto a system memory 304, a mass storage device 306, and a communicationmodule 308. System memory 304 provides processor 302 withnon-transitory, computer-readable storage to facilitate execution ofcomputer instructions by processor 302. Examples of system memory 304include random access memory (RAM) devices, such as dynamic RAM (DRAM),synchronous DRAM (SDRAM), solid state memory devices, and/or a varietyof other memory devices. Computer programs, instructions, and data arestored on mass storage device 306. Examples of mass storage device 306include hard discs, optical disks, magneto-optical discs, solid-statestorage devices, and/or a variety of other mass storage devices.Communication module 308 is operable to communicate information withvarious components of IC manufacturing entities, such as design house15, mask house 20, and IC fab 25 of IC manufacturing system 10. In FIG.10, communication module 308 allows SBO system 300 to communicate with amask making system 310 (such as e-beam lithography system 200 of FIG. 7)and a wafer making system 315 (such as lithography system 250 of FIG.8). Communication module 308 includes Ethernet cards, 802.11 WiFidevices, cellular data radios, and/or other communication devices forfacilitating communication of SBO system 300 with IC manufacturingentities.

SBO system 300 further includes an IC design layout module 320, a maskfracturing module 325, an IC data collection module 330, an ICmanufacturing database 335, an SBO model module 340, and an SBO processmodule 345, which are communicatively coupled to carry out an SBOprocess (such as SBO process 140). In operation, IC design layout module320 receives an IC design layout for a target wafer pattern (forexample, from design house 15) and prepares the IC design layout for anSBO process. In some implementations, IC design layout module 320modifies the IC design layout for the target wafer pattern, such asdescribed above with reference to block 130 of method 100 (FIG. 2). Insome implementations, IC design layout module 320 extracts portions ofthe IC design layout, such that the SBO process is performed usingselected portions of the IC design layout, which can significantlyincrease the speed of the SBO process. IC data collection module 330 isconfigured to collect, store, and maintain IC manufacturing data, suchas data from mask making processes associated with mask making system310 and wafer making processes associated with wafer making system 315.The IC manufacturing data can be stored in IC manufacturing database335. In some implementations, IC data collection module 330 analyzes thecollected IC manufacturing data. In some implementations, analyzing thecollected IC manufacturing data can include filtering out low quality ICmanufacturing data (such as data deemed not reliable) and/orconsolidating the manufacturing data into useful statistical ICmanufacturing information (such as averaging). In some implementations,for illustration purposes only, the collected IC manufacturing dataincludes e-beam blur information, resist characteristic information(such as CDs associated with resist patterns after developingprocesses), etching bias information (such as CDs of wafer patternsafter etching processes), and/or other useful IC manufacturing data.

SBO model module 340 is configured to build one or more SBO models usingIC manufacturing data, such as that stored by IC manufacturing database335. The SBO model collectively simulates a mask making process and awafer making process as a function of a mask shot map and anillumination source map. SBO model module 340 can store the one or moreSBO models in an SBO database (not shown). In some implementations, SBOmodel module 340 performs various operations of method 150, such asthose described with reference to block 154 and block 156. Inparticular, SBO model module 340 builds the SBO model using collected ICmanufacturing data and maintains the SBO model according to newlycollected IC manufacturing data, such that the SBO model is tuned tocompensate for changes in the mask making processes and the wafer makingprocesses. SBO process module 345 is configured to perform an SBOprocess (such as SBO process 140) using the SBO model, where the SBOprocess module 345 optimizes a given mask shot map and a givenillumination source map based on the IC design layout, therebyminimizing differences between a target wafer pattern defined by the ICdesign layout and a simulated final wafer pattern generated using thegiven mask shot map and the given illumination source map. SBO processmodule 345 can provide the optimized mask shot map to mask making system310 and the optimized illumination source map to wafer making system315. In some implementations, SBO process module 340 performs variousoperations of method 140, such as those described with reference to FIG.5. In some implementations, mask fracturing module 325 is configured togenerate a mask pattern, for example, by fracturing the IC design layoutinto mask regions (mask polygons) as described herein. The mask shot mapcan correspond with the mask pattern. For example, in someimplementations, a mask shot map generated by SBO process module 340defines exposure information, such as an exposure dose, for each maskregion of the mask pattern. In alternative implementations, maskfracturing module 325 can be eliminated, such that SBO process module345 generates the mask shot map for direct use by mask making system310.

Turning again to FIG. 2, in some implementations, SBO process 140 isimplemented for full-chip mask synthesis, using the IC design layout togenerate the mask shot map and the illumination source map.Alternatively, to reduce processing time, in some implementations, SBOprocess 140 uses portions of IC design layout for generating the maskshot map and the illumination source. FIG. 11 is a flowchart of a method400 for fabricating an integrated circuit (IC), which can be implementedby IC manufacturing system 10 of FIG. 1, according to various aspects ofthe present disclosure. In method 400, as described below, a wafermaking process uses an illumination source map generated by an SBOprocess using portions of an IC design layout, while a mask makingprocess uses a mask shot map generated by an inverse beam technology(IBT) process using the IC design layout. Method 400 can enhancelithography printability similar to method 100, while increasingthroughput compared to method 100. Since method 400 is similar in manyrespects to method 100, similar operations in FIG. 11 and FIG. 2 areidentified by the same reference numerals for clarity and simplicity.Additional steps can be provided before, during, and after SBO process140, and some of the steps described can be moved, replaced, oreliminated for additional embodiments of SBO process 140.

A wafer making process can begin with block 410 and block 430, wheremethod 400 includes receiving portions of an IC design layout for atarget wafer pattern, and optionally, modifying portions of the ICdesign layout for the target wafer pattern. Block 410 and block 430 aresimilar to block 110 and block 130 described above with reference tomethod 100, except block 410 and block 430 involve only a portion of theIC design layout. Accordingly, method 400 proceeds to SBO process 140,which generates an optimized illumination source map and an optimizedmask shot map using the portion of the IC design layout. Method 400proceeds with block 170, where a wafer making process is performed tofabricate a wafer using the optimized illumination source map.

A mask making process can begin with block 110 and block 130. Method 400proceeds to block 440, where an IBT process generates a mask shot mapm_(f(IBT)) (referred to herein as an IBT-generated mask shot map) usingthe IC design layout. For ease of discussion, block 440 is referred toas IBT process 440. IBT process 440 uses an IBT model that simulates afinal wafer pattern by collectively simulating a mask making process anda wafer making process as a function of a given mask shot map. In someimplementations, the IBT model is the same as the SBO model used in SBOprocess 140, though the following discussion is directed towardsimplementations where the IBT model and the SBO model implementdifferent parameters. Using the IBT model, IBT process 440 tunes themask shot map to minimize differences between an IBT-predicted finalwafer pattern P_(IBT) and target wafer pattern T defined by the ICdesign layout. The IBT model generates the predicted final wafer patternP_(IBT) as a function of the simulated mask making process and thesimulated wafer marking process, as expressed by:P _(IBT)(x,y)=Γ_(IBT)(I _(IBT)(Φ_(IBT)(m _(f(IBT))(x,y)))),  Equation(14)where a predicted final wafer pattern P_(IBT)(x, y) defines a contour ofa final wafer pattern formed in a wafer material layer generated by anIBT-simulated wafer making process, a wafer patterning function Γ_(IBT)defines lithography process characteristics associated with theIBT-simulated wafer making process, a projected wafer image functionI_(IBT) defines an image of a mask on a resist layer during an exposureprocess associated with the lithography process, a mask patterningfunction Φ_(IBT) defines lithography process characteristics associatedwith an IBT-simulated mask making process, and a mask shot mapm_(f(IBT))(x,y) defines an exposure pattern for fabricating the maskduring the IBT-simulated mask making process. The IBT model is furtherused in the IBT process to define an optimization (minimization) problemas expressed by:

$\begin{matrix}{{{\min\limits_{m_{f{({IBT})}}}{{P_{IBT} - T}}} = {\min\limits_{m_{f{({IBT})}}}{{{\Gamma_{IBT}\left( {I_{IBT}\left( {\Phi_{IBT}\left( {m_{f{({IBT})}}\left( {x,y} \right)} \right)} \right)} \right)} - T}}}},} & {{Equation}\mspace{14mu}(15)}\end{matrix}$where IBT process 440 tunes an exposure pattern of mask shot mapm_(f(IBT))(x,y) in a manner that minimizes the difference betweenIBT-predicted final wafer pattern P_(IBT)(x, y) and target wafer patternT. IBT process 440 and associated IBT model are described by U.S. patentapplication Ser. No. 14/832,026, filed Aug. 21, 2015, the entiredisclosure of which is incorporated herein by reference. IBT process 440can eliminate errors arising from stage-by-stage mask optimizationmethods, such as optical proximity correction (OPC) methods, inverselithography technology (ILT) methods, and/or mask process correction(MPC) methods. In some implementations, IBT process 440 can use theoptimized illumination source map generated by SBO process 140 duringIBT-simulated wafer making processes, though it is noted that IBTprocess 440 does not optimize illumination source optics information,such as those defined by illumination source maps. In someimplementations, where the IBT model and the SBO model use the sameparameters, the SBO process can generate a portion of the mask shot mapbased on the portion of the IC design layout, and the IBT process cangenerate the remaining portion of the mask shot map based on the entireIC design layout and/or the optimized mask layout generated by the SBOprocess. At block 160, method 400 includes fabricating a mask using themask shot map generated by IBT process 440, such as IBT-generated maskshot map m_(f(IBT))(x,y). In some implementations, the wafer makingprocess at block 170 uses the mask fabricated at block 160 inconjunction with the optimized illumination source map generated by SBOprocess 140.

Source beam optimization (SBO) processes are disclosed herein forenhancing lithography printability. SBO processes disclosed hereingenerate optimized exposure data for a mask making process and a wafermaking process, such as an optimized mask shot map and an optimizedillumination source map. In contrast to conventional lithographyoptimization processes, which do not consider mask making effects (suchas OPC processes, ILT processes, and/or source mask optimization (SMO)processes), SBO processes described herein optimize the exposure datacompensating for both mask making effects (caused, for example, by maskwriting blur and/or other mask making factors) and wafer making effects(caused, for example, by resist blur, mask diffraction (which isinfluenced by illumination source optics), projection imagingresolution, etching bias, and/or other wafer making processes). Byoptimizing both exposure sources, SBO significantly reduces (and caneven eliminate) variances between a final wafer pattern (such as finalwafer pattern 60) and a target wafer pattern provided by an IC designlayout (such as IC design layout 35), particularly compared toconventional lithography optimization processes, such as SMO. In someimplementations, SBO can replace or operate in conjunction with theother lithography optimization processes, such as OPC (which simulateonly wafer making processes for optimizing mask patterns only), ILT(which simulate only wafer making processes for optimizing mask patternsonly), and/or SMO (which simulate only wafer making processes foroptimizing mask patterns with illumination sources). In someimplementations, SBO can eliminate errors arising from stage-by-stagemask optimization processes, such as OPC, ILT, and/or MPC. Furthermore,SBO improves upon IBT processes by considering both an illuminationsource map and a mask shot map, thereby providing more optimizationfreedom. It is noted that different embodiments disclosed herein offerdifferent advantages and no particular advantage is necessarily requiredin all embodiments.

An exemplary method includes receiving an IC design layout andperforming an SBO process using the IC design layout to generate a maskshot map and an illumination source map. The SBO process uses an SBOmodel that collectively simulates a mask making process using the maskshot map and a wafer making process using the illumination source map. Amask can be fabricated using the mask shot map, and a wafer can befabricated using the illumination source map (and, in someimplementations, using the mask fabricated using the mask shot map). Thewafer includes a final wafer pattern that corresponds with a targetwafer pattern defined by the IC design layout. In some implementations,the SBO process generates the mask shot map and the illumination sourcemap that minimizes a difference between a predicted final wafer patternand a target wafer pattern, wherein the SBO process generates thepredicted final wafer pattern from the simulated mask making process andthe simulated wafer making process, and further wherein the target waferpattern is defined by the IC design layout. The SBO model simulates thefinal wafer pattern as defined as a function of the mask shot map andthe illumination source map, which are functions of a wafer patterningfunction, a mask patterning function, and a projected wafer imagingfunctions. The SBO process uses the SBO model to define an optimizationproblem that minimizes a difference between the simulated final waferpattern and the target wafer pattern. Exemplary relationships betweensuch functions and/or optimization (minimization) problems are describedin detail above. The SBO process can include adjusting the mask shot mapand illumination source map until a desired fit is achieved between thepredicted final wafer pattern and the target wafer pattern.

In some implementations, the method further includes fabricating a maskusing the mask shot map, wherein the mask includes a final mask patterncorresponding with a mask pattern associated with the mask shot map, andfurther wherein the mask pattern corresponds with a target wafer patterndefined by the IC design layout. In some implementations, the mask shotmap is an electron beam (e-beam) shot map, and fabricating the maskincludes performing an e-beam lithography process using the e-beam shotmap. In such implementations, the method can further include generatingthe mask pattern by fracturing the IC design layout into mask regions,wherein the e-beam shot map defines an exposure dose and/or an exposureshape for patterning each mask region on the mask. In someimplementations, the method further includes fabricating a wafer usingthe illumination source map, wherein the wafer includes a final waferpattern that corresponds with a target wafer pattern defined by the ICdesign layout. Fabricating the wafer can include performing an exposureprocess that illuminates a mask with illumination source optics definedby the illumination source map. The mask used during the exposureprocess can be fabricated using the mask shot map. In someimplementations, the SBO process is performed using a portion of the ICdesign layout to generate the mask shot map and the illumination sourcemap, and the method further includes fabricating a wafer using theillumination source map. In such implementations, the method can furtherinclude performing an inverse beam technology (IBT) process using the ICdesign layout to generate an IBT-generated mask shot map, wherein theIBT process uses an IBT model that collectively simulates a mask makingprocess and the wafer making process as a function of a given mask shotmap. In some implementations, the IBT model simulates the wafer makingprocess using an optimized illumination source map generated by the SBOprocess. Such implementations can further include fabricating a maskusing the IBT-generated mask shot map, wherein the mask is used whenfabricating the wafer.

Another exemplary method includes receiving an IC design layout defininga target wafer pattern, a mask shot map, and an illumination source map,and simulating a final wafer pattern based on the mask shot map and theillumination source map, wherein the simulating uses a source beamoptimization (SBO) model that collectively simulates a mask makingprocess using the mask shot map and a wafer making process using theillumination source map. The method can further include adjusting themask shot map and the illumination source map based on a fit between thesimulated final wafer pattern and the target wafer pattern, andgenerating an optimized mask shot map and an optimized illuminationsource map when the fit minimizes variances between the simulated finalwafer pattern and the target wafer pattern. The SBO model simulates thefinal wafer pattern as defined as a function of the mask shot map andthe illumination source map, which are functions of a wafer patterningfunction, a mask patterning function, and a projected wafer imagingfunctions. The SBO model further defines an optimization problem thatminimizes a difference between the simulated final wafer pattern and thetarget wafer pattern. Exemplary relationships between such functionsand/or optimization (minimization) problems are described in detailabove.

In some implementations, the method further includes fabricating a maskusing the optimized mask shot map, wherein the mask includes a finalmask pattern corresponding with a mask pattern associated with the maskshot map, and further wherein the mask pattern corresponds with thetarget wafer pattern. In some implementations, the method furtherincludes fabricating a wafer using the optimized illumination sourcemap, wherein the wafer includes a final wafer pattern that correspondswith the target wafer pattern defined by the IC design layout.Fabricating the wafer can include performing an exposure process thatilluminates the mask with illumination source optics defined by theoptimized illumination source map. In some implementations, the methodfurther includes generating the mask pattern by fracturing the IC designlayout into mask regions, wherein the mask shot map defines an exposuredose and/or an exposure shape for patterning each mask region on themask.

An exemplary source beam optimization (SBO) system for use in integratedcircuit (IC) manufacturing includes an IC manufacturing data collectionmodule configured to collect IC manufacturing data associated with maskmaking processes and wafer making processes; an SBO model moduleconfigured to build an SBO model using the manufacturing data, whereinthe SBO model collectively simulates a mask making process using a givenmask shot mask and a wafer making process using a given illuminationsource map; and an SBO process module configured to perform an SBOprocess using the SBO model to optimize the given mask shot map and thegiven illumination source map based on an IC design layout, therebyminimizing differences between a target wafer pattern defined by the ICdesign layout and a simulated final wafer pattern generated using thegiven mask shot map and the given illumination source map.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for enhancing lithography printability,the method comprising: receiving an integrated circuit (IC) designlayout; and performing a source beam optimization (SBO) process usingthe IC design layout to generate a mask shot map and an illuminationsource map, wherein the SBO process uses an SBO model that collectivelysimulates a mask making process using the mask shot map and simulates awafer making process using the illumination source map.
 2. The method ofclaim 1, wherein the SBO process generates the mask shot map and theillumination source map that minimizes a difference between a predictedfinal wafer pattern and a target wafer pattern, wherein the SBO processgenerates the predicted final wafer pattern from the simulated maskmaking process and the simulated wafer making process, and furtherwherein the target wafer pattern is defined by the IC design layout. 3.The method of claim 2, wherein the SBO model generates the predictedfinal wafer pattern as a function of the simulated mask making processand the simulated wafer marking process, as expressed by:P(x,y)=γ(1(S(x,y),Φ(m_(f)(x,y))), wherein: a predicted final waferpattern P(x, y) defines a contour of a final wafer pattern formed in awafer material layer generated by the simulated wafer making process, awafer patterning function Γ defines lithography process characteristicsof a lithography process associated with the simulated wafer makingprocess, a projected wafer image function I defines an image of a maskon a resist layer during an exposure process associated with thelithography process, an illumination source map S(x,y) definesillumination source optics for illuminating the mask during thesimulated wafer making process, a mask patterning function Φ defineslithography process characteristics associated with the simulated maskmaking process, and a mask shot map m_(f)(x,y) defines an exposurepattern for fabricating the mask during the simulated mask makingprocess.
 4. The method of claim 3, wherein the SBO model is used duringthe SBO process to define an optimization problem that minimizes thedifference between the predicted final wafer pattern and the targetwafer pattern as expressed by:${\min\limits_{S,m_{f}}{{P - T}}} = {\min\limits_{S,m_{f}}{{{\Gamma\left( {I\left( {{S\left( {x,y} \right)},{\Phi\left( {m_{f}\left( {x,y} \right)} \right)}} \right)} \right)} - T}}}$wherein P is the predicted final wafer pattern P(x, y) and T defines acontour of a target wafer pattern based on the IC design layout.
 5. Themethod of claim 4, wherein the SBO process includes adjusting mask shotmap m_(f) and illumination source map S until a desired fit is achievedbetween the predicted final wafer pattern and the target wafer pattern.6. The method of claim 1, further comprising fabricating a mask usingthe mask shot map, wherein the mask includes a final mask patterncorresponding with a mask pattern associated with the mask shot map, andwherein the mask pattern corresponds with a target wafer pattern definedby the IC design layout.
 7. The method of claim 6, wherein the mask shotmap is an electron beam (e-beam) shot map, and the fabricating the maskincludes performing an e-beam lithography process using the e-beam shotmap.
 8. The method of claim 7, further comprising generating the maskpattern by fracturing the IC design layout into mask regions, whereinthe e-beam shot map defines an exposure dose and/or an exposure shapefor patterning each mask region on the mask.
 9. The method of claim 1,further comprising fabricating a wafer using the illumination sourcemap, wherein the wafer includes a final wafer pattern that correspondswith a target wafer pattern defined by the IC design layout.
 10. Themethod of claim 9, wherein the fabricating the wafer includes performingan exposure process that illuminates a mask with illumination sourceoptics defined by the illumination source map.
 11. The method of claim10, wherein the mask used during the exposure process was fabricatedusing the mask shot map.
 12. The method of claim 1, wherein the SBOprocess is performed using a portion of the IC design layout to generatethe illumination source map.
 13. The method of claim 12, furthercomprising: performing an inverse beam technology (IBT) process usingthe IC design layout to generate an IBT-generated mask shot map, whereinthe IBT process uses an IBT model that collectively simulates a maskmaking process and a wafer making process that implements illuminationsource optics based on the illumination source map; fabricating a maskusing the IBT-generated mask shot map; and fabricating a wafer using themask and the illumination source map.
 14. A method for enhancinglithography printability, the method comprising: receiving an integratedcircuit (IC) design layout that defines a target wafer pattern;receiving a mask shot map and an illumination source map; in a sourcebeam optimization (SBO) process, simulating a final wafer pattern basedon the mask shot map and the illumination source map, wherein thesimulating uses an SBO model that collectively simulates a mask makingprocess using the mask shot map and simulates a wafer making processusing the illumination source map; adjusting the mask shot map and theillumination source map based on a fit between the simulated final waferpattern and the target wafer pattern; and generating an optimized maskshot map and an optimized illumination source map when the fit minimizesvariances between the simulated final wafer pattern and the target waferpattern.
 15. The method of claim 14, wherein the SBO model simulates thefinal wafer pattern as expressed by:P(x,y)=Γ(I(S(x,y),Φ(m _(f)(x,y))), wherein: a predicted final waferpattern P(x, y) defines a contour of a final wafer pattern formed in awafer material layer generated by the simulated wafer making process, awafer patterning function Γ defines lithography process characteristicsassociated with the simulated wafer making process, a projected waferimage function I defines an image of a mask on a resist layer during anexposure process associated with the lithography process, anillumination source map S(x,y) defines illumination source optics forilluminating the mask during the simulated wafer making process, a maskpatterning function Φ defines lithography process characteristicsassociated with the simulated mask making process, and a mask shot mapm_(f)(x,y) defines an exposure pattern for fabricating the mask duringthe simulated mask making process.
 16. The method of claim 15, whereinthe SBO model is used in the SBO process to define an optimizationproblem that minimizes a difference between the simulated final waferpattern and the target wafer pattern as expressed by:${\min\limits_{S,m_{f}}{{P - T}}} = {\min\limits_{S,m_{f}}{{{\Gamma\left( {I\left( {{S\left( {x,y} \right)},{\Phi\left( {m_{f}\left( {x,y} \right)} \right)}} \right)} \right)} - T}}}$wherein P is the predicted final wafer pattern P(x, y) and T defines acontour of the target wafer pattern based on the IC design layout. 17.The method of claim 14, further comprising: fabricating a mask using theoptimized mask shot map, wherein the mask includes a final mask patterncorresponding with a mask pattern associated with the mask shot map, andwherein the final mask pattern corresponds with the target waferpattern; and fabricating a wafer using the optimized illumination sourcemap and the mask, wherein the wafer includes a final wafer pattern thatcorresponds with the target wafer pattern defined by the IC designlayout.
 18. The method of claim 17, wherein the fabricating the waferincludes performing an exposure process that illuminates the mask withillumination source optics defined by the optimized illumination sourcemap.
 19. The method of claim 17, further comprising generating the maskpattern by fracturing the IC design layout into mask regions, whereinthe mask shot map defines an exposure dose and/or an exposure shape forpatterning each mask region of the mask regions on the mask.
 20. Asource beam optimization (SBO) system for use in integrated circuit (IC)manufacturing, the SBO system comprising: an IC manufacturing datacollection module configured to collect integrated circuit (IC)manufacturing data associated with mask making processes and wafermaking processes; an SBO model module configured to build an SBO modelusing the IC manufacturing data, wherein the SBO model collectivelysimulates a mask making process using a given mask shot map and a wafermaking process using a given illumination source map; and an SBO processmodule configured to perform an SBO process using the SBO model thatoptimizes the given mask shot map and the given illumination source mapbased on an IC design layout, thereby minimizing differences between atarget wafer pattern defined by the IC design layout and a simulatedfinal wafer pattern generated using the given mask shot map and thegiven illumination source map.